Investigation of the thermal runaway of silicon carbide diodes during blocking operation

Schottky-diodes in silicon (Si) are well-known for their problematic blocking behaviour at high temperatures and high blocking voltages. High leakage currents [1] and self-heating can lead to a thermal runaway [2] due to the fatal feedback loop of both. Devices produced of silicon carbide (SiC) are expected to avoid this problem by much lower leakage currents due to the higher Schottky barrier height [1]. Accordingly, this problem was supposed to be solved for good. However, early SiC-Schottky-diodes suffered from non-ideal leakage current densities [3] [4] [5] and were highly endangered by thermal runaway. In this work the blocking stability of current SiC-Schottky- and SiC-pin-diodes is investigated by means of calculation and measurement. Different leakage mechanisms in Schottky- and pin-diodes lead to different voltage and temperature dependencies of the leakage current. The temperature difference ΔT_d, for which a doubling of the leakage current I_R occurs, is significantly higher for SiC-Schottky- and SiC-pin-diodes at nominal voltage than for Si-pin-diodes. Experiments show, that the thermal stability is achieved even under worst cooling conditions or during high temperature operation and thermal runaway during blocking is no longer a limiting factor within the specified operating range. However, when going to higher voltages or operating temperatures the risk of thermal runaway has to be reassessed.